The present invention relates to a system for communicating between data processing systems and between units constituting a data processing system.
With the recent expansion in the variety of data processes, communication is carried out between data processing systems or between units constituting a data processing system.
Communication between units (apparatuses within the same system) or between adjacent systems, can be conducted through a memory commonly owned by those units.
In prior art systems data reading is carried out using a polling method. With this method, communication speed between units depends on the polling period, which limits the effectiveness of communication by the common memory. Therefore, a more effective communication method using a common memory is necessary. FIG. 1 shows a prior art communication system using a common memory.
According to the prior art common memory technology, a writable and readable memory is co-owned by a plurality of units (for example, unit A and unit B) 1 and a special meaning (for example, a command area or data area) is given to the predetermined address of the common memory 2.
When unit A1 intends to send something to unit B1, predetermined data such as commands are written in a predetermined address of the common memory by unit A1.
Unit B1 enables the data to be read out periodically from the previously defined address by using a well-known polling method and recognizes the above communication data transmitted from unit A1.
According to the communication system of the above prior art method, it is necessary for unit B1 to periodically perform polling to common memory 2. The communication speed depends on the polling period of unit B1 and therefore cannot reach the desired level.